Eased gate voltage restriction via body-bias voltage governor

ABSTRACT

An arrangement, to ease restriction upon gate voltage (Vgg) magnitudes for a dynamic threshold MOS (DTMOS) transistor, may include: an MOS transistor including a gate and a body; and a body-bias-voltage (Vbb) governor (Vbb-governor) circuit to provide a governed version of Vgg of the MOS transistor to the body of the MOS transistor as a dynamic body bias-voltage (Vbb).

BACKGROUND OF THE PRESENT INVENTION

Low threshold transistor logic, e.g., CMOS, is desirable because itfacilitates reducing the footprint of circuits, requires a smaller powersupply capability, etc. But low threshold voltage logic sufferssubstantial leakage current during a non-active mode that can, e.g.,negate the benefit of the reduced power consumption during an activemode.

The Background Art addressed the leakage problem with a multi-thresholdMOS (MTMOS) architecture, e.g., MTCMOS-type, that serially couples asleep transistor and a low threshold logic circuit between asystem-supply voltage (VDD) and a system-ground voltage (VSS). The sleeptransistor has a high threshold voltage and so exhibits low leakagecurrent in a sleep mode, but is slower to switch to the active mode thana comparable low-threshold transistor. As its name suggests, the sleeptransistor reduces the non-active mode current of the low-thresholddevice because it serially connects the low-threshold logic to VSS. Thesleep transistor imposes little in the way of a switching-speed penaltybecause it is always on during the active mode of the low-thresholdlogic.

High threshold voltages are typically achieved by applying a body biasvoltage (Vbb) to the sleep transistor. The requisite Vbb generatorcircuitry increases the foot print of the overall device. Also, the highthreshold of the sleep transistor requires a larger channel size toobtain comparable current capability, which also increases the overallfootprint.

The Background Art addressed the footprint problem associated with theVbb generator circuitry by using a dynamic threshold MOS (DTMOS)transistor as the sleep transistor. In a DTMOS transistor, the gate isconnected to the well (or, in other words, the transistor body), whichforward biases the source/body junction. This eliminates the need for aseparate Vbb generator circuit. As the gate voltage (Vgg) is used tobias the body, the threshold voltage varies with (or, in other words, isdynamic in proportion to) changes in the gate voltage.

Sub-threshold voltage leakage of a DTMOS transistor is generally low.But a high gate voltage which is also applied as Vbb can, in effect,forward bias one of the gate junctions (analogous to forward-biasing adiode) in the transistor and cause a forward-biased-diode-type leakagecurrent. This is generally depicted in the circuit diagram of BackgroundArt FIG. 3.

In Background Art FIG. 3, a leakage current path 302 is depicted. Therethe source, gate and body of a transistor 308 are connected to voltageVDD, which raises a node 304 is raised to voltage VDD. This has theeffect of raising Vgg and thus Vbb for an NMOS transistor 306 to beabout VDD, which forward biases the gate-source junction in NMOStransistor 306 and causes leakage.

Such junction forward-biasing can be solved by limiting Vgg to about 0.6volts, which in Background Art FIG. 3 necessarily limits VDD to about0.6 volts.

SUMMARY OF THE PRESENT INVENTION

At least one embodiment of the present invention provides an arrangementto ease restriction upon gate voltage (Vgg) magnitudes for a dynamicthreshold MOS (DTMOS) transistor. Such an arrangement may include: anMOS transistor including a gate and a body; and a body-bias-voltage(Vbb) governor (Vbb-governor) circuit to provide a governed version ofVgg of the MOS transistor to the body of the MOS transistor as a dynamicbody bias-voltage (Vbb).

Additional features and advantages of the invention will be more fullyapparent from the following detailed description of example embodiments,the accompanying drawings and the associated claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a block diagram of an sleep device to easerestriction upon gate voltage for a DTMOS transistor, according to atleast one embodiment of the present invention, the sleep device beingincorporated into an MTMOS (again, multi-threshold MOS), e.g., MTCMOS,architecture according to at least one other embodiment of the presentinvention.

FIG. 1B illustrates a block diagram of another sleep device to easerestriction upon gate voltage for a DTMOS transistor, according to atleast one other embodiment of the present invention, this sleep devicebeing incorporated into an MTMOS architecture according to at least oneother embodiment of the present invention.

FIG. 1C illustrates a block diagram of another MTMOS architecture thatis a combination of the MTMOS architectures of FIGS. 1A and 1B,according to at least one other embodiment of the present invention.

FIG. 2A is a circuit diagram of an example implementation of the sleepdevice in FIG. 1A (again, for easing restriction upon gate voltage for aDTMOS transistor), according to at least one other embodiment of thepresent invention.

FIG. 2B is a circuit diagram of an example implementation of the sleepdevice in FIG. 1B (again, for easing restriction upon gate voltage for aDTMOS transistor), according to at least one other embodiment of thepresent invention.

FIG. 3 is a circuit diagram illustrating a leakage-current problem for aDTMOS transistor circuit according to the Background Art.

Excluding FIG. 3, the drawings are: intended to depict exampleembodiments of the present invention and should not be interpreted tolimit the scope thereof. Relative proportion in the drawings may bereduced or exaggerated for clarity. In other words, the drawings are notto scale.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

In developing the present invention, the following problem with theBackground Art was recognized and a path to a solution identified. TheBackground Art prevents unwanted forward biasing of one of the gatejunctions in a DTMOS (again, dynamic threshold MOS) transistor byplacing a limit on the magnitude of VDD (again, the system-supplyvoltage), and consequently on the magnitude of Vgg (again, the gatevoltage). This is a simplistic solution that can at least frustrate, ifnot preclude, the use of one or more DTMOS transistors in circuits forwhich values of VDD and/or Vgg above a threshold voltage of the DTMOStransistor (e.g., about 0.6 volts, assuming that the DTMOS transistor isN-type) can (desirably) be present, which is a problem. An arrangementto impose an upper bound on the magnitude of Vbb (again the body biasvoltage), e.g., Vbb≦V_(sleep) ^(threshold), would ease restrictions uponVDD and/or Vgg, and thus solve the problem mentioned above. At least oneembodiment of the present invention provides such an arrangement.

FIG. 1A illustrates a block diagram of sleep device 104 to easerestriction upon gate voltage for a DTMOS transistor, according to atleast one embodiment of the present invention, sleep device 104 beingincorporated into an MTMOS (again, multi-threshold MOS), e.g., MTCMOS,architecture 100A according to at least one other embodiment of thepresent invention.

In FIG. 1A, architecture 100A includes: a circuit 102 that includes lowthreshold transistors (hereafter, LT-circuit 102); and sleep device 104(discussed in more detail below). LT-circuit 102 can be, e.g., a CMOScircuit including one or more low-threshold PMOS and one or morelow-threshold NMOS transistors. Alternatively, LT-circuit 102 can beformed solely of PMOS transistors or solely of NMOS transistors. A greatmany circuits can correspond to circuit 102, hence very little detailabout the internal construction of LT-circuit 102 is provided.

In architecture 100A, LT-circuit 102 and sleep device 104 are seriallyconnected between VDD (again, system-supply voltage) and VSS (again,system-ground voltage). More particularly, LT-circuit 102 is connectedbetween VDD and sleep device 104. And sleep device 104 is connectedbetween LT-circuit 102 and VSS.

Sleep device 104 includes: a DTMOS (again, dynamic threshold MOS)transistor QN1, e.g., of NMOS fabrication; and a body-bias-voltage(again, Vbb) governor (hereafter Vbb-governor) circuit 106 to provide adynamic body-bias voltage (Vbb) to the body of DTMOS transistor QN1.

Vbb-governor circuit 106 is arranged as a voltage divider that includesa first part and a second part coupled at a node 120. The voltage onnode 120 is provided to transistor QN1 as its Vbb. The first part canbe, e.g., a buffer circuit BUF2 that couples Vgg of transistor QN1 tonode 120. Additionally, buffer circuit BUF2 also can be coupled betweenVDD and VSS. The second part can be, e.g., a diode D2 that couples node120 to VSS. Diode D2 can be, e.g., a PMOS transistor whose gate anddrain are connected to VSS and whose source is connected to node 120(discussed further below), a PN junction connected between node 120 andVSS, a Schottky barrier connected between node 120 and VSS, etc.

While transistor QN1 is considered a DTMOS transistor because Vbb is afunction of Vgg, sleep device 104 differs from the Background Artbecause Vbb is not merely Vgg connected substantially directly to thebody of transistor QN1. Instead, Vbb is a governed version of Vgg: Agoverned version of a signal has had at least one of an upper and alower bound imposed upon it, which is analogous to a clipped signalalbeit without the connotation of noise associated withsaturation-induced clipping. In other words, Vbb can be dependent, e.g.,non-linearly dependent, upon Vgg. Here, the terms “governor, “governed,”etc. are to be understood in a context that is analogous to the term“governor” in the automotive art. There, a governor is a device thatautomatically prevents the speed or position of some part (e.g., enginespeed, transmission speed, etc) from exceeding a maximum desired value.

Here, Vbb-governor circuit 106 is operable to impose a bound (e.g., herean upper bound because transistor QN1 is N-type) on the magnitude of Vbb(|Vbb|_(bound)) such that a there can be a non-negligible difference Δbetween a corresponding bound of Vgg (e.g., here, an upper bound becausetransistor QN1 is N-type, |Vgg|_(bound)=|Vgg|_(max)) and |Vbb|_(max),Δ=∥Vgg| _(max) −|Vbb| _(max)|.  1)And further because transistor QN1 is N-type,|Vbb| _(max) ≦|Vgg| _(max).  2)

Difference Δ (also referred to as the “Vgg margin”) is greater than orequal to a threshold (or, in other words, turn-on) voltage of diode D2,

$\begin{matrix}{\Delta \geq {V_{D\; 2}^{thresh}.}} &  3 )\end{matrix}$For example, |Vgg|_(bound)=|Vgg|_(max)≦1.2 volts while |Vbb|_(max)≈0.6volts.

The operation of Vbb-governor circuit 106, in an active mode, can bedescribed according to the following relation.

$\begin{matrix}{{{Vbb}}_{\max} \approx \{ \begin{matrix}{{Vgg},} & {{{for}\mspace{14mu}{VSS}} \leq {Vgg} \leq V_{D\; 2}^{threshold}} \\{V_{D\; 2}^{threshold},} & {{{for}\mspace{14mu} V_{D\; 2}^{threshold}} < {Vgg}}\end{matrix} } &  4 )\end{matrix}$An effect of the operation of Vbb-governor circuit 106 is tosubstantially stabilize Vbb against fluctuations in Vgg.

FIG. 1B illustrates a block diagram of another sleep device 108 to easerestriction upon gate voltage for a DTMOS transistor, according to atleast one other embodiment of the present invention, where sleep device108 is incorporated into an MTMOS architecture 100B according to atleast one other embodiment of the present invention.

In FIG. 1B, architecture 100B includes: circuit 102; and sleep device108 (discussed in more detail below). In architecture 100B, LT-circuit102 and sleep device 108 are serially connected between VDD and VSS.More particularly, sleep device 108 is connected between VDD andLT-circuit 102. And LT-circuit 102 is connected between sleep device 104and VSS.

Sleep device 104 includes: a DTMOS transistor QP4, e.g., of PMOSfabrication; and a Vbb-governor circuit 110 to provide a dynamic Vbb tothe body of transistor QP4. Vbb-governor circuit 110 is similar toVbb-governor circuit 104 of FIG. 1A.

Vbb-governor circuit 110 is arranged as a voltage divider that includesa first part and a second part coupled at a node 122. The voltage onnode 122 is provided to transistor QP4 as its Vbb. The first part canbe, e.g., a buffer circuit BUF1 that couples Vgg of transistor QP4 tonode 122. Additionally, buffer circuit BUF1 also can be coupled betweenVDD and VSS. The second part can be, e.g., a diode D1 that couples node122 to VDD. Diode D1 can be, e.g., an NMOS transistor whose gate anddrain are connected to VDD and whose source is connected to node 122(discussed further below), a PN junction connected between VDD and node122, a Schottky barrier connected between VDD and node 122, etc.

While transistor QP4 is considered a DTMOS transistor because Vbb is afunction of Vgg, sleep device 108 differs from the Background Artbecause Vbb is not merely Vgg connected substantially directly to thebody of transistor QP4. Instead, Vbb is a governed version of Vgg. Inother words, again, Vbb can be dependent, e.g., non-linearly dependent,upon Vgg. Vbb-governor circuit 110 is operable to impose a bound (e.g.,here a minimum bound because transistor QP4 is P-type,|Vbb|_(bound)=|Vbb|_(min)) such that there can be (as with Vbb-governorcircuit 104) the non-negligible difference Δ between the correspondingvalue of Vgg (e.g., here, a minimum value because transistor QP4 isP-type) |Vgg|_(bound)=|Vgg|_(min) and |Vbb|_(min). Further, becausetransistor QP4 is P-type,|Vgg| _(min) ≦|Vbb| _(min).  5)For example, |Vgg|_(bound)=|Vgg|_(min)≈0 volts while|Vbb|_(min)≈VDD−V_(D1) ^(threshold).

The operation of Vbb-governor circuit 110, in an active mode, can bedescribed according to the following relation.

$\begin{matrix}{{{Vbb}}_{\min} \approx \{ \begin{matrix}{{Vgg},} & {{{for}\mspace{14mu}( {{VDD} - V_{D\; 1}^{threshold}} )} \leq {Vgg} \leq \approx {VDD}} \\{{{VDD} - V_{D\; 1}^{threshold}},} & {{{for}\mspace{14mu}{Vgg}} < {{VDD} - V_{D\; 1}^{threshold}}}\end{matrix} } &  6 )\end{matrix}$An effect of the operation of Vbb-governor circuit 110 (as withVbb-governor circuit 106) is to substantially stabilize Vbb againstfluctuations in Vgg.

FIG. 1C illustrates a block diagram of another MTMOS architecture 100Cthat is a combination of the MTMOS architectures 100A of FIGS. 1A and100B of 1B, according to at least one other embodiment of the presentinvention.

Architecture 100C includes a serial connection of LT-circuit 102 andboth of sleep devices 104 and 108 between VDD and VSS. Moreparticularly, sleep device 104 is connected between LT-circuit 102 andVSS. And sleep device 108 is connected between VDD and LT-circuit 102.Further description of architecture 100C would be repetitive of thatpresented above and is omitted for the sake of brevity.

FIG. 2A is a circuit diagram of an example implementation of sleepdevice 104 in FIG. 1A (again, for easing restriction upon gate voltagefor DTMOS transistor QN1), according to at least one other embodiment ofthe present invention.

In FIG. 2A, buffer circuit BUF2 includes a pair of inverters connectedbetween VDD and VSS. More particularly, the first inverter can be a pairof serially-connected transistors, e.g., a PMOS transistor QP2 and anNMOS transistor QN2. Similarly, the second inverter can be another pairof serially-connected transistors, e.g., a PMOS transistor QP3 and anNMOS transistor QN3.

The source of transistor QP2 can be connected to VDD and its drainconnected to the drain of transistor QN2 at a node 202. The source oftransistor QN2 can be connected to VSS. The gates of transistors QP3 andQN3 also can be connected to node 202. The source of transistor QP3 canbe connected to VDD and its drain connected to the drain of transistorQN3 at a node 204. The source of transistor QN3 can be connected to VSS.Node 204 is connected as Vbb for DTMOS transistor QN1. Hence, node 204corresponds to node 120 of FIG. 1A. The gates of transistors QP2 and QN2can be connected together at a node 206, which can be connected to thegate of DTMOS transistor QN1.

Diode D2 is connected between node 204 and VSS. More particularly, diodeD2 in FIG. 2A is depicted as a PMOS transistor P7 whose source isconnected to node 204 and whose gate and drain are connected to VSS.

The operation of the circuitry of FIG. 2A will now be discussed.

In an active mode, namely when Vgg2 for DTMOS transistor QN1 is raisedabove V_(QN1) ^(threshold), then so is the voltage on node 206, whichcauses transistor QP2 to turn-off and transistor QN2 to turn-on. As aresult, the voltage on node 202 is reduced to about VSS. This causestransistor QN3 to turn-off and transistor QP3 to turn-on, whichinitially raises the voltage on node 204 in proportion to increases inVgg2 (starting at V_(gg)≈VSS). The clipping effect of diode-configuredtransistor P7, however, places an upper bound on the voltage at node 204as follows

$\begin{matrix}{V_{node204} \approx {{VSS} + V_{p\; 7}^{threshold}}} &  7 )\end{matrix}$while transistor QP3 is on and transistor QN3 is off. As such, Vbb is nolonger effected by the degree to which Vgg2 is raised above

V_(P 7)^(threshold) = V_(D 2)^(threshold).If VSS=0, then

$\begin{matrix}{V_{{node}\; 204} = {V_{QN1}^{bb} \approx {V_{P\; 7}^{threshold}.}}} &  8 )\end{matrix}$

In a non-active or sleep mode, namely when Vgg2 for DTMOS transistor QN1is set low, e.g., Vgg₂≈VSS, then so is the voltage on node 206, whichcauses transistor QP2 to turn-on and transistor QN2 to turn-off. As aresult, the voltage on node 202 is raised to

$\begin{matrix}{V_{{node}\; 202} \approx {{VDD} - V_{{QP}\; 2g}^{threshold}}} &  9 )\end{matrix}$This causes transistor QN3 to turn-on and transistor QP3 to turn-off,which reduces the voltage on node 204 to about VSS, namely

$\begin{matrix}{V_{{node}\; 202} \approx {{VSS} + V_{{QN}\; 3g}^{threshold}}} &  10 )\end{matrix}$

FIG. 2B is a circuit diagram of an example implementation of sleepdevice 108 in FIG. 1B (again, for easing restriction upon gate voltagefor DTMOS transistor QP4), according to at least one other embodiment ofthe present invention.

In FIG. 2B, buffer circuit BUF1 includes a pair of inverters connectedbetween VDD and VSS. More particularly, the first inverter can be a pairof serially-connected transistors, e.g., an NMOS transistor QN5 and aPMOS transistor QP5. Similarly, the second inverter can be another pairof serially-connected transistors, e.g., a PMOS transistor QP6 and anNMOS transistor QN6.

The source of transistor QP5 can be connected to VDD and its drainconnected to the drain of transistor QN5 at a node 208. The source oftransistor QN5 can be connected to VSS. The gates of transistors QP6 andQN6 also can be connected to node 208. The source of transistor QP6 canbe connected to VDD and its drain connected to the drain of transistorQN6 at a node 210. The source of transistor QN6 can be connected to VSS.Node 210 is connected as Vbb for DTMOS transistor QP4. Hence, node 210corresponds to node 122 of FIG. 1A. The gates of transistors QN5 and QP5can be connected together at a node 212, which can be connected to thegate of DTMOS transistor QP4.

Diode D1 is connected between VDD and node 210 More particularly, diodeD1 in FIG. 2B is depicted as an NMOS transistor N7 whose gate and drainare connected to VDD and whose source is connected to node 210.

The operation of the circuitry of FIG. 2B will now be discussed.

In an active mode, namely when Vgg4 for DTMOS transistor QP4 is set low,then so is the voltage on node 212, which causes transistor QN5 toturn-off and transistor QP5 to turn-on. As a result, the voltage on node208 is raised to about VDD. This causes transistor QP6 to turn-off andtransistor QN6 to turn-on, which reduces the voltage at node 210initially in proportion to decreases in Vgg (starting from Vgg₄≈VDD).The clipping effect of diode-configured transistor N7, however, places alower bound on the voltage at node 210 while transistor QN6 is on andtransistor QP6 is off, as follows.

$\begin{matrix}{V_{{node}\; 210} = {V_{{QP}\; 4}^{bb} \approx {{VDD} - V_{N\; 7}^{threshold}}}} &  11 )\end{matrix}$As such, Vbb is no longer effected by the degree to which Vgg4 isreduced below

V_(N 7)^(threshold) = V_(D 1)^(threshold).

In an non-active or sleep mode, namely when Vgg4 for DTMOS transistorQP4 is set high, e.g., Vgg_(QP4)≈VDD, then so is the voltage on node212, which causes transistor QN5 to turn-on and transistor QP5 toturn-off. As a result, the voltage on node 208 is reduced to

$\begin{matrix}{V_{{node}\; 208} \approx {{VSS} + V_{{QN}\; 5g}^{threshold}}} &  12 )\end{matrix}$This causes transistor QP6 to turn-on and transistor QN6 to turn-off,which reduces the voltage on node 210 to about VDD, namely.

$\begin{matrix}{V_{{node}\; 210} = {V_{{QP}\; 4}^{bb} \approx {{VSS} + V_{{QN}\; 6g}^{threshold}}}} &  13 )\end{matrix}$

Of course, although several variances and example embodiments of thepresent invention are discussed herein, it is readily understood bythose of ordinary skill in the art that various additional modificationsmay also be made to the present invention. Accordingly, the exampleembodiments discussed herein are not limiting of the present invention.

1. An arrangement to ease restriction upon gate voltage (Vgg) magnitudesfor a dynamic threshold MOS (DTMOS) transistor, the arrangementcomprising: an MOS transistor including a gate and a body; and abody-bias-voltage (Vbb) governor (Vbb-governor) circuit to provide agoverned version of Vgg of the MOS transistor to the body of the MOStransistor as a dynamic body bias-voltage (Vbb); wherein theVbb-governor circuit includes at least a voltage-divider circuitconnected between a gate of the MOS transistor and a system voltage;wherein the voltage-divider circuit includes a first part and a secondpart connected at a first node, the body of the MOS transistor beingconnected to the first node; wherein the first part is a buffer circuit;and wherein the second part is a diode circuit.
 2. The arrangement ofclaim 1, wherein the Vbb-governor circuit is further operable to imposea boundary value on a magnitude of Vbb (|Vbb|_(bound)) such that thereis a non-negligible difference between |Vbb|_(bound) and a correspondingboundary value on a magnitude of Vgg (|Vgg|_(bound)).
 3. The arrangementof claim 2, wherein the difference is referred to as Δ and Δ is greaterthan or equal to a threshold voltage of the diode circuit,Δ ≤ V_(diode)^(thresh).
 4. The arrangement of claim 3, wherein thesystem voltage is a system ground voltage.
 5. The arrangement of claim4, wherein: the second part of the voltage divider circuit includes thediode circuit connected between the first node and the system-groundvoltage.
 6. The arrangement of claim 4, wherein: the MOS transistor isan NMOS transistor; and the diode circuit includes at least one of thefollowing a PMOS transistor whose gate and drain are connected to thesystem-ground voltage and whose source is connected to the first node, aPN junction connected between the first node and the system-groundvoltage, and a Schottky barrier connected between the first node and thesystem-ground voltage.
 7. The arrangement of claim 1, wherein: the diodecircuit includes a PMOS transistor whose gate and drain are connected toa system-ground voltage and whose source is connected to the first node.8. The arrangement of claim 1, wherein the system voltage is a systemsupply voltage.
 9. The arrangement of claim 8, wherein: the second partof the voltage divider circuit includes a diode circuit connectedbetween the first node and a system-supply voltage.
 10. The arrangementof claim 8, wherein: the MOS transistor is a PMOS transistor; and thediode circuit includes at least one of the following an NMOS transistorwhose gate and source are connected to the first node and whose drain isconnected to the system-supply voltage, a PN junction connected between,the system-supply voltage and the first node, and a Schottky barrierconnected between the system-supply voltage and the first node.
 11. Thearrangement of claim 9, wherein: the diode circuit includes an NMOStransistor whose gate and source are connected to the first node andwhose drain is connected to the system-supply voltage.
 12. Anarrangement to ease restriction upon gate voltage (Vgg) magnitudes for adynamic threshold MOS (DTMOS) transistor, the arrangement comprising: anMOS transistor including a gate and a body; and a body-bias-voltage(Vbb) governor circuit to provide a dynamic body bias-voltage (Vbb) tothe body of the MOS transistor, the body bias-voltage Vbb beingdifferent than but related to a gate voltage (Vgg) of the MOStransistor, the Vbb-governor circuit being operable to substantiallystabilize Vbb against fluctuations in the Vgg of the MOS transistor, theVbb governor-circuit including a first part and a second part connectedat a first node, the body of the MOS transistor being connected to thefirst node; wherein the first part is a buffer circuit; and wherein thesecond part is a diode circuit.
 13. The arrangement of claim 12, whereinthe Vbb-governor circuit is further operable to impose a boundary valueon a magnitude of Vbb (|Vbb|_(bound)) such that there is anon-negligible difference between |Vbb|_(bound) and a correspondingboundary value on a magnitude of Vgg (|Vgg|_(bound)).
 14. Thearrangement of claim 13, wherein the difference is referred to as Δ andΔ is greater than or equal to a threshold voltage of the diode circuit,Δ ≤ V_(diode)^(thresh).
 15. A dynamic threshold MOS (DTMOS) transistorarrangement comprising: an MOS transistor including a gate and a body;and a voltage-divider circuit connected between a gate of the MOStransistor and a system voltage; the voltage-divider circuit including afirst part and a second part connected at a first node, the body of theMOS transistor being connected to the first node; wherein the first partis a buffer circuit; and wherein the second part is a diode circuit. 16.The arrangement of claim 15, wherein, at the first node, the diodecircuit represents a significantly smaller resistance than the buffercircuit.
 17. A dynamic threshold MOS (DTMOS) transistor arrangementcomprising: an MOS transistor including a gate and a body; and avoltage-divider circuit connected between a gate of the MOS transistorand a system voltage; the voltage-divider circuit including a first partand a second part connected at a first node, the body of the MOStransistor being connected to the first node; and wherein the first partincludes a pair of series-connected inverters.
 18. A multi-threshold MOS(MTMOS) transistor arrangement comprising: a subject circuit thatincludes low threshold-voltage transistors for which leakage current isto be controlled; and a current cut-off (CCS) switch circuit thatincludes an MOS transistor having a gate and a body, and abody-bias-voltage-governor (Vbb-governor) circuit to provide a governedversion of Vgg of the MOS transistor to the body of the MOS transistoras a dynamic body bias-voltage (Vbb), the Vbb-governor circuit includinga first part and a second part connected at a first node, the body ofthe MOS transistor being connected to the first node; the first partbeing a buffer circuit; the second part being a diode circuit; and thesubject circuit and the CCS switch circuit being serially connectedbetween a system-supply voltage (Vdd) and a system-ground voltage (Vss).19. The arrangement of claim 18, wherein the Vbb-governor circuit isfurther operable to impose a boundary value on a magnitude of Vbb(|Vbb|_(bound)) such that there is a non-negligible difference between|Vbb|_(bound) and a corresponding boundary value on a magnitude of Vgg(|Vgg|_(bound)).
 20. The arrangement of claim 18, wherein arrangementtakes one of the following configurations: the subject circuit isconnected to Vdd and the Vbb-governor circuit is connected to Vss; andthe Vbb-governor circuit is connected to Vdd and the subject circuit isconnected to Vss.
 21. The arrangement of claim 18, wherein: theVbb-governor circuit has upper and lower parts; and the upper part isconnected between Vdd and the subject circuit; and the lower part isconnected between the subject circuit and Vdd.
 22. An apparatus to easerestriction upon gate voltage (Vgg) magnitudes for a dynamic thresholdMOS (DTMOS) transistor, the apparatus comprising: an MOS transistorincluding a gate and a body; and a body-bias-voltage governor means forgenerating a dynamic body bias-voltage (Vbb) and providing the Vbb tothe body of the MOS transistor, the governor means further being forproviding a governed version of the Vgg to the body of the MOStransistor as the dynamic body bias-voltage (Vbb), the governor meansyet further including buffer means and diode means connected at a firstnode, the body of the MOS transistor being connected to the first node.23. The apparatus of claim 22, wherein the governor means further is forimposing a boundary value on a magnitude of Vbb (|Vbb|_(bound)) suchthat there is a non-negligible difference between |Vbb|_(bound) and acorresponding boundary value on a magnitude of Vgg (|Vgg|_(bound)). 24.The apparatus of claim 23, wherein the difference is referred to as Δand Δ is greater than or equal to a threshold voltage of the diode,Δ ≥ V_(diode)^(thresh).